Every industry faces the problem of mistakes found in their products. These are whether human or machine-made mistakes. Most often the defective products are "collected" by the quality control inspectors or they can also be filtered by persons who monitor and work in finished products packaging departments.

Defective products are instantly destroyed as soon as spotted. However, this is not the case of money, defective money. It is worth mentioning that the United States Mint has several facilities that produce and issue billions of coins each year. The Philadelphia and Denver Mints have the biggest share in U.S. coin production. Both produce about 40 million coins per day while others, including the specialized West Point and San Francisco Mints, go second.

Taking into consideration the huge amount of coins mined, this undoubtedly means a lot of errors. Note that modern mintage of coins is performed at a very high rate, such that a human eye hardly perceives coins' strike. Today some of the fastest presses known to the world are able to press coins at a speed of 10 coins per second.

In case there are coins with errors, these can be spotted only when they fall into the receiving hopper. Although such process is performed on an occasional basis, very few coins, from those millions produced and issued daily in the United States, are being checked, most of them coming into circulation without being visually inspected.

In order to prevent the issue or even the production of error coins, each minting coins facility in the United States has installed so-called riddling devices. These are filters that eliminate planchets with smaller or bigger sizes, as well as mis-shaped coins. Though such sifters should prevent error coins from being put into circulation, they still are unable to work 100 percent right. There are slightly mis-shaped or a little bit oversized coins that are able to pass through the riddling devices. Interesting to note, sometimes error coins find their way out of the coining facility not by mistake. This is because employees sometimes sell such coins to collectors for a nice profit.

Such gasp for error coins began not so long ago. For many centuries people considered such coins as simply curiosities, these being worth much less than ordinary coins. Coins containing errors were put under the FIDO's mark, meaning freaks, irregulars, defective and oddities. Only in the seventh decade of the 20^th century people started hunting for error coins to make them a part of personal collection. During that time people established clubs devoted to error coins. After that error coins significantly increased their value and collectors began studying how these errors were produced, thus increasing the general knowledge of the minting process as a whole.

Coin collectors and dealers put error coins under three headings: planchet, die or strike. Such system, shorter named P-D-S, is really not hard to remember. In addition it can be used for almost all coins containing one error. However, there are cases when some coins have more than one error. Imagine a coin which was struck by a defective planchet, which lead to a mis-strike. This means that the error coin suits two headings: P and S. Most often, though, coins fall only under one heading.